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Sensitivity analysis, modeling of
axial air drag
The purpose of the sensitivity analysis is to determine how the
numerical solution is affected by changes in the constants for calculation of
axial air drag.
Background
The fly line will be subject to shear stresses in the axial or
lengthwise direction as it travels through the air. What is referred to as
boundary layers form in the vicinity of the fly line. The properties of the
boundary layers determine the axial air drag. A fly line will, in general, move
at an angle in the air. The angle will influence the boundary layer increasing
the shear stresses and the drag compared to a boundary layer developing along a
line at zero angle. Here, the air drag is calculated as a function of the
Reynolds number based on experimental data. The increase in shear stress due to
the angle is accounted for approximately. Hence, there is uncertainty in the
calculation of axial air drag.
Method
The sensitivity of the solution to changes in axial air drag is
analyzed as follows:
·
The 50ft
oh ref. cast is used as reference (drag
constants as for all calculated casts except the one below).
· A solution, denoted “50ft ax drag flyline +50%”, is calculated with
a 50% increased axial air drag as the only change in relation to the reference
cast.
Results
The two solutions are compared in the
animation below (click on image to start animation).
· Increasing the axial air drag by 50%, in relation to the
reference, has a significant impact on the simulated cast.
· The calculation of axial air drag introduces a degree of
uncertainty.